The current invention is concerned with the record and replay of stored information. In common magnetic information storage systems, the information is usually recorded along a line called a track. During replay, it is necessary to accurately follow the information track with a playback transducer. Various methods of following the information track, or "tracking", are used in information storage systems. The scheme in which the tracks are placed may affect the method of tracking. For example, tracks on computer disks follow concentric paths, and tracks on video tape are linear and are adjacent to each other. One linear format, called helical-scan format, is most commonly used with video cassette recorders, VCRs. The recording medium in VCRs, usually a long continuous tape, may have been recorded on a machine that is different from the playback machine. Tracking systems must therefore be machine independent. To accomplish machine independent tracking, a portion of the recording medium is reserved for a control track. The control track, which is free from playback information, has position information encoded on it to help the tracking system correctly position the tape with respect to the playback transducer scan path. The control track requires space on the magnetic tape that could otherwise be used for information. It is a disadvantage to use the recording medium in this way because it limits the amount of useful information that can be stored on a cassette. The information in the control track is read by a second transducer called a servo head which is dedicated to this purpose. The electronics to support the dedicated servo head, the servo head, and the extra space required by the control track on the recording medium, are all necessary for many tracking systems.
Depending upon the application, the degree of accuracy required of the tracking mechanism varies. Some of the newer formats used for recording and playing of information at very high bandwidth, require higher recording densities at higher track densities and at higher head velocities.
Some such systems have an improved tracking system, which also has the benefit of eliminating the wasted space of a control track. The control information consists of deep-layer low frequency tone recordings, usually beneath and between the information tracks, which are recorded at high density, near the surface of the media. This scheme provides separation between the servo and the information. Some such systems still require Pre-formatting of the recording medium.